[FEA]: Identify and fix/report issues with MultiLineString.crosses

[thomcom]

Is this a new feature, an improvement, or a change to existing functionality?

New Feature

How would you describe the priority of this feature request

Critical (currently preventing usage)

Please provide a clear description of problem you would like to solve.

This issue is that a MultiLineString made from two identical linestrings changes its crosses result as opposed to using the linestrings individually.

from shapely.geometry import LineString, MultiLineString
l1 = LineString([(0, 0), (1, 1)])
l2 = LineString([(0, 0), (1, 1)])
l = LineString([(0, 1), (0, 0), (1, 0)])
m = MultiLineString([l1, l2])
print(l1.crosses(l))
print(l2.crosses(l))
print(m.crosses(l))

False
False
True

Because I'm writing test generators that build a variety of tests from more basic inputs, I'm seeing this occur a few times in cases where a MultLineString a is created via duplicating another LineString b twice: a = MultiLineString([b, b]).

I'm confused because the problem doesn't occur if the LineStrings that comprise a have no intersection:

a = LineString([(0, 1), (0, 0), (1, 0)])
b = LineString([(0, 0.75), (1, 0.75)])
c = LineString([(0, 0.25), (1, 0.25)])
display(GeometryCollection([a, b, c]))
print(a.crosses(b))
print(a.crosses(c))
print(a.crosses(MultiLineString([b, c])))
print(a.crosses(MultiLineString([b, b])))
print(a.crosses(MultiLineString([c, c])))

However, if the LineStrings that make up a share a vertex, and that vertex intersects with l, then it seems like the LineStrings are combined into a single LineString, then crosses is computed. Anyway I'm just taking some notes here and reporting on my progress.

a = LineString([(0, 1), (0, 0), (1, 0)])
b = LineString([(0, 0), (1, 1)])
c = LineString([(0, 0), (1, 0.5)])
display(GeometryCollection([a, b, c]))
print(a.crosses(b))
print(a.crosses(c))
print(a.crosses(MultiLineString([b, c])))
print(a.crosses(MultiLineString([b, b])))
print(a.crosses(MultiLineString([c, c])))

False
False
True
True
True

As you can see, the crosses result of a MultiLineString is not taking the and or or result of crosses on all the individual LineStrings.

Describe any alternatives you have considered

No response

Additional context

No response

[harrism]

The title of this issue is very vague. Can you better summarize the request in the title?